The conventionally known three-dimensional wiring boards include an MID (Molded Interconnect Device) substrate that is a component in which an electric circuit is directly and three-dimensionally formed on a surface of a structural body having a three-dimensional structure. Processes such as the two shot molding process, MIPTEC (Microscopic Integrated Processing Technology), and LDS (Laser Direct Structuring) are known as technology that relates to MID substrates. In each of these processes, after forming mold resin into a three-dimensional structure, a wiring circuit is formed on a surface thereof. For example, in Patent Document 1, technology relating to an MID substrate and the production thereof is disclosed.
In the two shot molding process, secondary molding is performed using new resin with respect to a portion which is not subjected to wiring formation on mold resin that underwent primary molding, and catalyst application and plating is then performed using the resin relating to the secondary molding as a resist to thereby form a wiring circuit on the mold resin. However, because of limitations to the mold machining precision for the secondary molding in order to regulate a wiring pattern shape by means of the resin that is subjected to the secondary molding, the minimum value for L/S (line width and spacing) that indicates the conductor width and conductor spacing is of the order of 150/150 μm, and formation of a finer wiring pattern has been difficult.
In MIPTEC, metallizing is performed with respect to the entire surface of the mold resin that was molded, and metal (a metallized layer) at an outer edge portion of the wiring circuit is removed by means of a laser beam. Subsequently, electroplating is performed by passing an electric current through a region that is to serve as a wiring circuit, and thereafter flash etching is performed with respect to the whole area of the molded body to remove metal other than the wiring circuit and thereby form the wiring circuit on the mold resin. However, in the case of using a laser beam, a special laser irradiation apparatus that corresponds to the three-dimensional shape of the mold resin that was molded is required, and the time and labor required for laser machining as well as an increase in the production cost that is caused by investment in plant and machinery is a problem. Further, since it is necessary to pass a current through only a region that is to serve as a wiring circuit in order to deposit metal that is required for the wiring circuit by electroplating, it is necessary for the region that is to serve as the wiring circuit to be electrically connected to an outer circumferential portion of the molded body or to be electrically connected to the outer circumferential portion through a power feeder line. That is, the problems arise that it is difficult to electrically isolate the region that serves as the wiring circuit from the outer circumferential portion of the molded body (that is, to form an independent wiring pattern), and that the costs increase accompanying formation and removal of a power feeder line that is ultimately not required for the circuit.
In LDS, a wiring circuit is formed on mold resin by performing primary molding using a special resin material that contains conductive particles, irradiating a laser beam onto a region that is to serve as a wiring circuit to expose the conductive particles, and performing plating at a portion at which the conductive particles are exposed. However, because of a problem regarding the accuracy with which conductive particles within the mold resin that was molded are exposed, the minimum value of the L/S is of the order of 100/150 μm, and formation of a finer wiring pattern has been difficult. Further, similarly to MIPTEC, a special laser irradiation apparatus is required, and the time and labor required for laser machining as well as an increase in the production cost that is caused by investment in plant and machinery are problems.
Further, in each of the above described processes, because a wiring circuit is formed on mold resin having a three-dimensional shape, the MID substrate that is ultimately produced is a single-sided substrate. Therefore, the problem arises that the degree of freedom with respect to the wiring circuit is less when compared to a double-sided substrate, and miniaturization of the substrate is also difficult. As a method for solving this problem and the problems described above, a method of producing a three-dimensional wiring board is available in which a wiring circuit is formed on thermoplastic resin such as polyimide, and thereafter the resin is subjected to bending work by heating and pressurization. For example, Patent Document 2 discusses performing three-dimensional molding after a metal foil is attached onto a polyimide film by thermocompression bonding, and Patent Document 3 discusses performing three-dimensional molding after applying a conductive paste onto polysulfone resin.